diff --git a/src/testdir/test_tabline.vim b/src/testdir/test_tabline.vim
index 5560a21..e58a412 100644
--- a/src/testdir/test_tabline.vim
+++ b/src/testdir/test_tabline.vim
@@ -134,6 +134,17 @@
   set tabline=
 endfunc
 
+" When there are exactly 20 tabline format items (the exact size of the
+" initial tabline items array), test that we don't write beyond the size
+" of the array.
+func Test_tabline_20_format_items_no_overrun()
+  set showtabline=2
 
+  let tabline = repeat('%#StatColorHi2#', 20)
+  let &tabline = tabline
+  redrawtabline
+
+  set showtabline& tabline&
+endfunc
 
 " vim: shiftwidth=2 sts=2 expandtab